After a day of slower-than-expected preparations in the Chukchi Sea, Shell Alaska officially began drilling into the seafloor above its Burger prospect at 4:30 a.m. Sunday, the company said.

The action marks the first drilling offshore in the Alaska Arctic in two decades and is being closely watched by Alaskans and the oil industry -- and criticized by environmentalists.

A YouTube video posted by Shell shows the drill bit, labeled Shell Burger "A" and dated Sept. 8, creeping down from the ship's center into the gray sea as the operation got under way Saturday. The drilling machinery clanked and whirred.

By 6:30 a.m. Sunday, crews had drilled more than 300 feet into the ground for a narrow pilot hole that will eventually be about 1,400 feet deep, Shell spokesman Curtis Smith said. It's used to check for unexpected natural gas pockets, oil or obstructions before a wider hole is drilled.

The actual drilling was supposed to begin mid-day Saturday but Shell and its contractors took time to reposition the drilling apparatus and make other adjustments, Smith said. A tool attached to the drill bit will allow Shell to collect data on the formation, density, pressures and other key attributes.

"Everything just took a little bit longer than they thought. There was certainly no rush," Smith said. "There was a collective thought that they were going to double- and triple-check everything."

Greenpeace, which earlier this summer had a research ship near the prospect site, said Shell's drilling began "after a summer of near-disasters and costly delays."

Shell began to drill almost two months later than planned because a key safety vessel, the oil spill containment barge Arctic Challenger, wasn't finished. It remains at a shipyard in Bellingham, Wash. It is scheduled to leave the dock Sunday evening for two to three days of inspections at sea by the Bureau of Safety and Environmental Enforcement.

The Interior Department granted Shell a drilling permit that requires it to stop far short of oil-rich zones until the Challenger is in place.

Shell also notified regulators it couldn't meet some limits on air pollution emissions specified in an Environmental Protection Agency permit. The EPA issued a one-year order allowing Shell to operate, and said overall emissions should fall under the already approved cap.

In July, Shell's Chukchi drilling rig, the Noble Discoverer, dragged anchor while at Dutch Harbor. It wasn't damaged, and the Coast Guard cleared the ship to head to the Arctic.

Shell won't be able to complete a single well in the Chukchi Sea this year unless the Interior Department grants its request for an extended season. It still is waiting to hear back. As it stands, Shell must stop drilling into oil-rich zones by Sept. 24.

"Whatever Shell is able to do in the narrow window between now and when the sea ice returns, it won't erase the clear evidence we've seen in the past two months that there's no such thing as safe drilling in the Arctic," Dan Howells of Greenpeace said in a written statement.

Greenpeace is pushing a campaign to put attention on global warming and "save the Arctic," which it says is melting.

"The company's Arctic drilling program this summer has not only been an epic PR failure, but a dangerous logistical failure as well," Howells, who is the organization's deputy campaigns director, said. "They've only proven one thing this summer, that oil companies are simply not equipped to deal with the unique challenges of operating in the Arctic."

Earlier this year, Greenpeace activists including actress Lucy Lawless boarded the Noble Discoverer in New Zealand to protest Shell's Arctic drilling. Shell responded by going to court for a restraining order to keep Greenpeace away from its Arctic drilling vessels.

Shell says Greenpeace's assessment is dead wrong and the group is hurting its own cause.

"Important conversations are taking place in regards to the future of the Arctic and organizations like this one have, in essence, excluded themselves because of their illegal activities and reliance on mistruths," Smith said.

The burden is on Shell to perform safely and it is doing that, with intense oversight by regulators, he said. Two federal inspectors with the Bureau of Safety and Environmental Enforcement are on drilling rig and others from the Environmental Protection Agency are set to come, he said.

"Ours is the most scrutinized exploration plan in the history of North America if not the world," Smith said.

Shell has invested close to $5 billion in its quest to drill in the Alaska Arctic. A federal government assessment last year estimated the Alaska Arctic offshore region holds nearly 27 billion barrels of "undiscovered technically recoverable" oil.